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Pandemic strain of Austropuccinia psidii confirmed as the cause of myrtle rust in New Zealand

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Formerly known as the Forest Research Institute, Scion has been a leader in research relating to forest health for over 50 years. The Rotorua-based Crown Research Institute continues to provide science that will protect all forests from damage caused by insect pests, pathogens and weeds. The information presented below arises from these research activities.

From Forest Health News 287, March 2019.

The pandemic strain of Austropuccinia psidii has been confirmed as the cause of myrtle rust in New Zealand in a recent paper by researchers at FABI (University of Pretoria, South Africa) and MPI (du Plessis, et al., 2019). Researchers used genetic markers called microsatellites to compare the New Zealand population to reference isolates from around the world. The pandemic strain is one of only two found outside of Central and South America (thought to be the native range of the pathogen). It is the strain that has been reported causing significant damage to Myrtaceae rich ecosystems in Australia, New Caledonia, and other areas of the Pacific over the last decade. The only other strain reported outside the native range is a strain found in South Africa. Several other strains are known in the native range, with some evidence of between-strain variation in behaviour and host range. For example, strains in Brazil and neighbouring countries cause significant damage to Eucalyptus and Psidium (guava) which so far seem more resistant to the pandemic strain.

Another important finding of the study was that there was high genotypic variation in the New Zealand population of A. psidii. Ten genotypes were detected across twenty individuals, collected from three hosts at the start of the incursion in 2017, Lophomyrtus bullata (ramarama), Metrosideros excelsa (pohutukawa) and M. kermadecensis (Kermadec pohutukawa). This could be a sign that sexual reproduction and recombination may play a role in the life cycle of myrtle rust in New Zealand. This would increase the adaptability of the pathogen population, increasing the possibility of change compared to purely clonal reproduction, with important implications for management. A sexually reproducing pathogen is more likely to both break down host resistance and to develop resistance against chemical or biological control methods. The importance of sexual reproduction in the New Zealand population of A. psidii is the focus of current research contributing to the MBIE funded Beyond Myrtle Rust Programme.

Stuart Fraser (Scion) and Alistair McTaggart (University of Queensland)

du Plessis E, Granados GM, Barnes I, Ho WH, Alexander BJR, Roux J, McTaggart AR (2019). The pandemic strain of Austropuccinia psidii causes myrtle rust in New Zealand and Singapore. Australasian Plant Pathology. doi:10.1007/s13313-019-0624-x


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